1. Field of Invention
This invention relates to manually powered impact stapling and tacking machines.
2. Description of Prior Art
Manually powered impact type stapling and tacking machines are well known. Such devices generally comprise a body, an energy storage spring, a fastener feeding system, a movable operating handle to deflect the energy storage spring, a mechanism to rapidly disengage the handle from the deflected spring, and a sliding plunger linked to the spring to impact the fastener.
The prior art demonstrates numerous means to link the operating handle to the mechanism of the machine. Typically the handle is hinged near the front of the body, front being the end from which the staple exits. To move the handle, the user presses downward and rearward with the palm of the hand. A second configuration has the handle and gripping portion of the tool body reversed so that the handle is pulled upward with the fingers while the palm of the hand presses downward upon the body. Either configuration is limited in utility because of the manner in which the forces must be applied by the operating hand.
By the first arrangement the operating hand must press toward the rear of the tool since leverage is available on the handle only behind the frontwardly mounted handle pivot. Therefore, to effectively install a fastener with this arrangement, a second hand is often required to push on the front of the tool to press the fastener into the installation point. The second hand also serves to prevent the staple exit end of the tool body from jumping away from the ejecting staple. Efficient one handed operation of such prior art staple guns is not possible. To press down upon the front end, the single operating hand must move closer to the handle pivot point. However, such a position reduces the leverage available to deflect the energizing spring.
Abrams U.S. Pat. No. 2,617,215 attempts to address this issue by placing the handle pivot further toward the front of the body and adding various linkages to enable such a handle to lift the plunger. The extreme forward pivot placement allows for leverage on the handle at a more forward position on the tool body. However, Abrams' design only marginally improves upon the prior art to allow efficient one hand operation.
In this configuration, a single hand may both pull the operating handle and push forward on the tool body. But since the operating handle must be pulled by just the finger, the power of the user's arm is not available to compress the energy storage spring in the tool.
Libert U.S. Pat. No. 2,769,174 and Krantz U.S. Pat. No. 2,326,540 approach a solution to the force application issue by placing the operating handle pivot at the rear of the tool body. However, these versions retain the typical front mounted energy storage spring and linkages. The hand grip of the tool must therefore be set back from the front to allow space to accommodate the spring and related linkages. These versions therefore only partially address the issue of efficient force application. The designs of Libert and Krantz do not allow the user's hand to push the handle from a position directly over the exiting staple. Hence they do not fully realize benefits from a rearwardly hinged handle design.
Prior innovations comprise use of plastic, or stamped metal combined with plastic, to form the body of a staple gun. The goal of the prior efforts was to take advantage of the formability and low cost of plastic. Plastic has been added to mostly stamped metal housings to provide a more comfortable hand grip.
Fealey, U.S. Pat. No. 4,452,388 claims a staple gun which is constructed of a "molded plastic body . . . between sheet metal sides." Fealey cites several prior art uses of molded plastic and notes that molded plastic "simplifies assembly" but that too much plastic causes "clearly some sacrifice in the reliability and durability of the device."
Ewig, U.S. Pat. No. 4,184,620, shows a stapler where the housing frame is formed of plastic to "provide the major support and guide elements." Such a tool will be low cost and may readily provide compound curves in the grip opening region. However, such a tool feels light weight and flimsy, provides poor shock damping, wears poorly and generally feels low quality. Such all plastic tools will not be considered "professional" and in fact are presently sold only as "economy" products.
Judge, U.S. Pat. No. 4,629,108, shows a housing of stamped metal enveloped by plastic covers. The outside shape can thereby be aesthetically pleasing and comfortable. The metal frame provides the structural function while the plastic provides the form.
Michkelsson, U.S. Pat. No. 4,126,260, shows a plastic insert added to a stamped housing to provide a contoured hand grip. This feature is presently common in other stapled gun products.
Prior workers have clearly recognized the advantage and disadvantage of molded plastic in staple guns. However, the prior art does not realize the solution to this dilemma, a die cast metal staple gun housing.
Steiner et. al. U.S. Pat. No. 4,640,451, described a desk top stapler and hole punch which may be die cast. Similarly U.S. Pat. No. 3,630,428 discloses a desk top stapler with a die cast base. A die cast main body and base are further disclosed in U.S. Pat. No. 2,136,374 for a heavy duty desk top stapler.
Smith et. al., U.S. Pat. No. 4,204,622, shows a power tool with a die cast housing. Such a housing is common among power tools.